1. Field of the Invention
The present invention relates generally to sound reproducing apparatus and, more particularly, is directed to a sound reproducing apparatus which is automatically made operative at a preset time for reproducing sound with a selected volume.
2. Description of the Prior Art
Sound reproducing apparatus has been proposed for receiving an audio signal from a broadcast radio receiver, an audio disk of tape player or other audio signal source and for reproducing sound based on such audio signal, and wherein a time control is provided for automatically controlling the main power supply and other operating components of the sound reproducing apparatus to start and stop at predetermined or present times. Such known sound reproducing apparatus is further provided with a remote controller by which the main power supply can be activated and other operations can be made to start or stop in response to command signals issued from a remote location.
In the known sound reproducing apparatus provided with the time control and remote control functions described above, the volume of the sound reproduced it response to the time control or the remote controller is controlled by varying the effective resistance value of a variable resistor which, for example, is included in an audio amplifier of an audio signal processing circuit, and which is controlled by a volume control signal. The variable resistor for effecting volume control can be electronically controlled, for example, in the form of a semi-conductor resistive device with its variable resistance controlled directly by a control signal, or it can be a mechanically driven variable resistor in the form of a rotary or linearly slidable variable resistive device provided with an actuator, such as, an electric motor, which drives the rotary or linearly slidable variable resistive device in response to a control signal.
The above described known sound reproducing apparatus provided with time control and remote control functions may be employed as an alarm for waking a sleeping person, in which case the time control function commences operation of the audio signal processing circuit for producing the sound output at a preset time, and the variable resistor is employed for obtaining the reproduced sound with an appropriate volume, that is, loud enough to wake a sleeping person.
For causing the volume controlling variable resistor to operate so that an appropriate volume of the reproduced sound is obtained from the apparatus provided with both the time control and remote control functions when used as an alarm for waking a person, it is necessary to recognize or sense the condition of the volume controlling variable resistor when the preset time is being established, and also at such preset time, that is, when the variable resistor becomes operative for obtaining the desired volume control. When the volume controlling variable resistor is constituted by an electronically controlled semi conductor resistive device having its variable resistance controlled directly by a control signal, the recognition and estimate of the resistance value of the volume controlling variable resistor can be easily achieved, at any time, on the basis of the control signal which is applied to the semi-conductor resistive device.
On the other hand, when a mechanically driven rotary or linearly slidable variable resistor is used for achieving the volume control, it is necessary to provide a device for detecting positions of a slider of the variable resistive device for use in recognizing and estimating the effective resistance value of the volume controlling variable resistor. Such slider position detecting device produces a detection output signal corresponding to the position of the slider of the sliding variable resistive device, and hence to its effective resistance value, and a circuit arrangement including a waveform shaping circuit, an analog-to-digital converter, a pulse counter and so on, for processing the detection output signal. The foregoing arrangement is disadvantageous in that it undesirably increases the complexity and cost of the sound reproducing apparatus.